1. Field of the Invention
The present invention generally relates to a method for detecting a hotspot in a photolithographic image. In particular, the present invention is directed to a method for detecting a hotspot in a photolithographic image according to aerial image intensity-related indices.
2. Description of the Prior Art
Electric circuits, for example integrated circuits (IC), are widely used in various electronic products, such as cars, microwave ovens, or personal computers. The design and fabrication of an IC component involves many steps, and sometimes it is called a design flow. A particular step in a design flow usually depends on the types, the complexity, the design team, the manufacturer or the foundry of the electric circuit. By executing a software simulation program and/or a hardware emulation program, a software tool or a hardware tool is used to exam the design of each stage in a design flow. These examining steps help to find out errors in the design so as to be corrected or improved by the designers or by the engineers.
With the designers and manufacturers continuously increasing the numbers of the circuit elements in each unit area and decreasing the sizes of the circuit elements, the patterns for the circuit elements formed on a substrate are getting smaller and smaller as well as closer and closer to one another. The shrinkage of the critical dimension of the circuit elements makes it harder and harder to fabricate the desirable layout patterns on the substrate. Diffraction of light may partially account for the cause of defects during the lithographic process so that the desirable images fail to be precisely formed on the substrate, and further the defects land in the final element structures.
So far, resolution enhancement techniques (RETs) are used to improve the resolution of the patterns of the mask on the substrate during the lithographic process. For example, an optical proximity correction (OPC) adjusts the amplitude of light passing through a reticle to change the image data of the layout pattern which is set for generating a reticle. For example, the rim of a layout pattern is often adjusted by such techniques to enlarge or to shrink some geometric parts by estimating the overexposure (or the underexposure) of a certain point on a substrate to alter the critical dimension (CD, or namely line width) of a certain part. Apt calibrations of the adjustment greatly improve the overall image fidelity.
However, what is insufficient is that, some layout regions still have imaging problems in spite of the above resolution enhancement techniques. These problematic regions are known as hotspots in this industrial field. The issue of the hotspots can only be corrected by changing the original layout design to alter the profile of the final patterns. For example, hotspots of pinching type are needed to be eliminated by increasing the width of the object's profile while hotspots of bridging type are needed to be eliminated by increasing the space between the profiles of two adjacent objects. The amending flow can be done at the manufacturer's end or at the designer's end. For the former part, the flow may sometimes be called ‘retarget’ because it involves the adjustment of the drawn patterns which lead to the final electric pattern on a wafer. Although the optical proximity correction or a process window simulation may serve as a guidance of retargeting, the entire amending flow is time-consuming and expensive. Accordingly, the industrial field is still looking for a new technique which is capable of more efficiently locating hotspots and amending a layout design.